# A Case of Trisomy 9 Mosaicism Diagnosed Following Detection of Placental Trisomy 9

## TL;DR

A rare case of trisomy 9 mosaicism was diagnosed in a newborn after placental testing revealed trisomy 9 linked to fetal growth restriction.

## Contribution

This case highlights the importance of placental chromosome analysis in diagnosing rare chromosomal conditions in newborns.

## Key findings

- Trisomy 9 was detected in the placenta due to fetal growth restriction.
- The neonate was diagnosed with trisomy 9 mosaicism with minimal clinical symptoms.
- Placental testing can reveal chromosomal abnormalities not evident in the newborn.

## Abstract

We report a case in which fetal growth restriction was observed during pregnancy. A placental chromosomal analysis was performed to investigate the cause of the fetal growth restriction and it showed trisomy 9. Prompt chromosomal testing of the neonate led to the diagnosis of trisomy 9 mosaicism. Although the neonate was small for gestational age and had mild respiratory distress and feeding difficulties, her clinical symptoms were minimal. Trisomy 9 mosaicism is extremely rare and shows considerable variability in its clinical presentation. This case report is important because trisomy 9 was detected by a placental chromosome analysis that was conducted to investigate the cause of fetal growth restriction. Additionally, a newborn with mild clinical findings was unexpectedly diagnosed with trisomy 9 mosaicism.